1. Technical Field
The present invention relates to a plasma display device and, more particularly, to a plasma display device having an assembly for efficiently discharging heat generated by a plasma display panel (PDP) to the exterior of the plasma display device.
2. Related Art
A PDP of a plasma display device displays images thereon using plasma generated by gas discharge. The PDP generates much heat during operation as a result of the high-temperature discharge gas. Further, if the amount of discharge is increased in an effort to improve brightness, an even greater amount of heat is generated in the plasma display device. This heat must be efficiently discharged to the exterior of the device to enable good operation of the same.
Therefore, in the conventional plasma display device, the PDP is attached to a chassis base made of a high thermal-conductivity material, and a heat discharge sheet (or a thermal conduction sheet) is interposed between the PDP and the chassis base. The heat discharge sheet and the chassis base expel the heat generated by the PDP to the exterior of the device. The chassis base is typically manufactured through a die casting process or a press process using a metal material, while the heat discharge sheet is made of an acryl- or silicone-based resin.
Many different configurations have been suggested to improve the heat discharge efficiency of heat discharge sheets. The following describes one such configuration.
A cushioning material is attached along the circumference of the panel, and then a liquid thermal conduction material is applied to the region surrounded by the shock-absorbing material. The thermal conduction material is then hardened. Next, the display panel is attached to the solid thermal conduction material to thereby realize a plasma display panel that promotes heat discharge efficiency. Such a structure is disclosed in Japanese Laid-Open Patent No. Hei 10-172446.
However, a drawback of this configuration is that the thermal conduction material has an isotropic structure that exhibits the same thermal conduction characteristics in all directions. As a result, it is difficult to minimize localized temperature differences caused by variations in image patterns.
Further, a plasma display device is disclosed in Japanese Laid-Open Patent No. Hei 11-251777 in which a thermal conduction sheet is interposed between a PDP and a thermal conduction plate (chassis base), while heat pipes, heat discharge pins, and a heat discharge plate are mounted on a rear surface of the thermal conduction plate. The plasma display device realizes a uniform distribution of heat through this structure. However, such a structure runs counter to efforts to obtain a slim profile and minimize noise generation.
In cases wherein there are differences in the image pattern, heat may be concentrated at specific areas and bright image sticking may result. “Bright image sticking” relates to a situation wherein a localized area on the screen stays momentarily brighter than its surroundings after a relatively bright image has been displayed in this localized area. An example of how bright image sticking may be generated is described with reference to FIG. 5. As one can see from FIG. 5, after a full white pattern was continuously displayed on the screen of a PDP 50 for 20 minutes, 3% window pattern A, a white region in which 3% load ratio is provided, is displayed for 10 minutes. Then, if a full white pattern is again displayed on the screen, a difference in brightness occurs between two portions corresponding to window pattern A and its surrounding area B, respectively. The 3% window pattern A refers to a white region in which a load ratio of as much as 3% is provided. This is a result of the phosphor illumination operation being affected by temperature. The difference in temperature between the 3% window pattern A and the surrounding area B is particularly large when the bright image sticking starts, and this temperature difference becomes even larger with increases in a peak brightness.
The generation of bright image sticking reduces picture quality. Therefore, there is a need for heat discharge sheets that provide for a greater thermal conductivity in the planar direction than in the thickness direction of PDP such that heat therefrom can be spread more uniformly so as to realize a more uniform heat distribution of the same.